Chlorates are produced electrolytically by the electrolysis of an aqueous solution of the corresponding chloride in a diaphragmless cell between anode and cathode electrodes. Sodium chlorate is the most common product produced by such process. The process involves the intermediate formation of hypochlorite ions (OCl.sup.-) which undergo decomposition to the chlorate ion (ClO.sub.3.sup.-).
Hexavalent chromium ions, usually introduced in the form of sodium dichromate, are present in the cell to prevent the reduction of the hypochlorite ions at the cathode, and the consequent loss of efficiency which otherwise would result. As a result, however, the sodium chlorate solution contains small amounts of hypochlorite ions, which need to be removed before the sodium chlorate solution enters the crystallizer, wherein sodium chlorate is recovered in crystalline form, or a storage area for later shipment as cell liquor.
The removal of hypochlorite, commonly termed "dehypoing", usually is effected by heating the cell liquor in a dehypo tank to remove the bulk of the hypochlorite by conversion to chlorate, with further removal being effected by treatment of the heated solution with urea or similar chemical. The chemical dehypoing process is time consuming, which introduces storage problems and capital expenditure. In addition, there have been reports of explosions when urea has been used.